Really I don't understand this. Ichigo had his entire Shihakusho intact after the fight with Byakuya.So he didn't lose even a bit of Reiatsu during the fight? The same is true when Aizen beat him with one finger. So I am not really sure what kind of chance he stands if Aizen has already defeated him in such a manner with all his reiatsu (reiatsu that didn't deplete a bit with after his fight against Byakuya???!!).
http://www.onemanga.com/Bleach/174/13/
Ichigo charging at Aizen with all of his reiatsu supposedly....
Really Kubo just came up with this idea all of a sudden without any thought as to what he had already written before. Unless it is the case that Ichigo was such a terrible fighter back then that he got beat up and exhausted much prior to depleting ANY of his reiatsu.